Information processing device, information processing method, and storage medium

ABSTRACT

An information processing device is configured to identify a background area of a first image registered from a first account and a background area of a second image registered from a second account, and to output identicalness information indicating whether a user owning the first account and a user owning the second account are identical to each other based on the background area of the first image and the background area of the second image.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority from Japanese application JP2020-161820 filed on Sep. 28, 2020, the content of which is herebyincorporated by reference into this application.

FIELD OF THE INVENTION

The present invention relates to an information processing device, aninformation processing method, and a storage medium.

BACKGROUND OF THE INVENTION

Various services are provided online. Users create their accounts inorder to use the services, and use the services through use of thecreated accounts. General users each create one account for one service,but some users may each create a plurality of accounts for one service.In order to grasp how the accounts are being used, a service operatorperforms processing for detecting a plurality of accounts created by anidentical user.

In JP2013-122630A, there is disclosed a technology for calculating amatching degree through use of profile information on a plurality ofaccounts and determining whether or not users of the accounts are anidentical person based on the calculated matching degree. In addition,in WO 2019/234827 A1, there is disclosed a technology for identifyingaccounts owned by an identical user based on profile information onaccounts and positional information identified by, for example, geo-tagsposted by the users of the accounts. In addition, in JP2017-151574A,there is disclosed a technology for comparing pieces of informationposted by users on social media and identifying an identical user basedon the match or similarity of, for example, frequently used words orphrases in posts, input habits, and posted content.

With the related-art methods, it may not be possible to detect aplurality of accounts created by an identical user. For example, when auser registers a plurality of accounts through use of different kinds ofprofile information and positional information, or when a service hardlyreflects the user's characteristics in posted text, it is difficult todetect a plurality of accounts created by an identical user.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above-mentionedproblem, and an object thereof is to provide a technology for detectinga plurality of accounts created by an identical user even when thedetection is difficult by a related-art method.

In order to solve the above-mentioned problem, according to at least oneembodiment of the present invention, there is provided an informationprocessing device including: a background identification moduleconfigured to identify a background area of a first image registeredfrom a first account and a background area of a second image registeredfrom a second account; and an information output module configured tooutput identicalness information indicating whether a user owning thefirst account and a user owning the second account are identical to eachother based on the background area of the first image and the backgroundarea of the second image.

Further, according to at least one embodiment of the present invention,there is provided an information processing method including:identifying a background area of a first image registered from a firstaccount and a background area of a second image registered from a secondaccount; and outputting identicalness information indicating whether auser owning the first account and a user owning the second account areidentical to each other based on the background area of the first imageand the background area of the second image.

Further, according to at least one embodiment of the present invention,there is provided a program for causing a computer to function as: abackground identification module configured to identify a backgroundarea of a first image registered from a first account and a backgroundarea of a second image registered from a second account; and aninformation output module configured to output identicalness informationindicating whether a user owning the first account and a user owning thesecond account are identical to each other based on the background areaof the first image and the background area of the second image.

In at least one embodiment of the present invention, the informationoutput module may be configured to: acquire a plurality of first localfeature vectors each indicating a local feature of the first image;acquire a plurality of second local feature vectors each indicating alocal feature of the second image; and output the identicalnessinformation based on results of searching for the second local featurevectors that correspond to the plurality of first local feature vectors,respectively. In at least one embodiment of the present invention, thebackground identification module may be configured to identify thebackground area of the first image and the background area of each of aplurality of second images, the information output module may beconfigured to select a plurality of candidate images each having thebackground area similar to the background area of the first image fromamong the plurality of second images based on a first global featurevector extracted from the first image and a plurality of second globalfeature vectors extracted from the plurality of second images,respectively, and the information output module may be configured to:acquire the plurality of first local feature vectors, each indicatingthe local feature of the first image and the plurality of second localfeature vectors, each indicating the local feature of any one of theplurality of candidate images; and output the identicalness informationindicating whether the user owning the first account and the user owningthe second account are identical to each other.

In at least one embodiment of the present invention, the informationoutput module may be configured to: estimate a three-dimensionalpositions for each of a plurality of points, at which at least a part ofthe plurality of first local feature vectors are extracted, based onpositions at which at least a part of the plurality of first localfeature vectors have been extracted in the first image and positions atwhich the second local feature vectors corresponding to the plurality offirst local feature vectors, respectively, have been extracted in thesecond image; and output the identicalness information based on theestimated three-dimensional positions of the plurality of points.

In at least one embodiment of the present invention, the backgroundidentification module may be configured to identify a background area ofat least one first image and a background area of each of a plurality ofsecond images, and the information output module may be configured to:search for at least one of second images corresponding to the at leastone first image based on the background area of the at least one firstimage and the background areas of the plurality of second images; andoutput the identicalness information based on the at least one of secondimages corresponding to the at least one first image.

In at least one embodiment of the present invention, the identicalnessinformation may be a result of determination of whether the user owningthe first account and the user owning the second account are identicalto each other.

In at least one embodiment of the present invention, the identicalnessinformation may indicate a magnitude of a probability that the userowning the first account and the user owning the second account areidentical to each other.

According to at least one embodiment of the present invention, it ispossible to detect a plurality of accounts created by the identical usereven when the detection is difficult by a related-art method.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram for illustrating an example of an informationprocessing system according to at least one embodiment of the presentinvention.

FIG. 2 is a block diagram for illustrating functions implemented by theinformation processing system.

FIG. 3 is a flow chart for illustrating an example of processing of animage registration module.

FIG. 4 is a view for illustrating an example of an image to beregistered.

FIG. 5 is a flow chart for illustrating an example of processing of abackground identification module and a feature extraction module.

FIG. 6 is a view for illustrating an example of a background image.

FIG. 7 is a view for schematically illustrating extraction of localfeature vectors.

FIG. 8 is a diagram for illustrating an outline of processing of anidenticalness information generation module.

FIG. 9 is a flow chart for illustrating an example of the processing ofthe identicalness information generation module.

FIG. 10 is a flow chart for illustrating an example of processing of anidenticalness information output module.

FIG. 11 is a flow chart for illustrating an example of the processing ofthe identicalness information output module.

FIG. 12 is a view for illustrating correspondences between first andsecond local feature vectors.

FIG. 13 is a view for illustrating calculation of a three-dimensionalposition.

FIG. 14 is a diagram for illustrating an example of correspondencesbetween first images and second images.

DETAILED DESCRIPTION OF THE INVENTION

Now, at least one embodiment of the present invention is described withreference to the accompanying drawings. Duplicate descriptions areomitted for each component denoted by the same reference symbol. In thisembodiment, there is described an information processing systemconfigured to provide a service in which a plurality of accounts arecreated by a plurality of users, posts of a plurality of images arereceived from each of the plurality of accounts, and the images are madepublic to users who access the images from other accounts.

FIG. 1 is a diagram for illustrating an example of an informationprocessing system 1 according to at least one embodiment of the presentinvention. The information processing system 1 includes an informationprocessing server 10 and an image storage 19. The information processingserver 10 is configured to communicate with at least one of customerterminals 2 and register, in the service, an image transmitted by a useroperating each customer terminal 2. Specifically, the informationprocessing system 1 stores an image received from the user in the imagestorage 19, and registers the image in a searchable manner.

The information processing server 10 includes a processor 11, a storage12, a communication unit 13, and an input/output unit 14. Theinformation processing system 1 may be implemented by a plurality ofserver computers configured to execute processing of the informationprocessing server 10.

The processor 11 is configured to operate in accordance with a programstored in the storage 12. The processor 11 is also configured to controlthe communication unit 13 and the input/output unit 14. Theabove-mentioned program may be provided through, for example, theInternet, or may be provided by being stored and provided in a flashmemory, a DVD-ROM, or another computer-readable storage medium.

The storage 12 is formed of memory devices, such as a RAM and a flashmemory, and an external storage device, such as a hard disk drive. Thestorage 12 is configured to store the above-mentioned program. Thestorage 12 is also configured to store information and calculationresults that are input from the processor 11, the communication unit 13,and the input/output unit 14.

The communication unit 13 implements a function of communicating withanother device, and is formed of, for example, an integrated circuit fora wireless LAN or a wired LAN. Under control of the processor 11, thecommunication unit 13 inputs information received from another device tothe processor 11 and the storage 12, and transmits information toanother device.

The input/output unit 14 is formed of, for example, a video controllerconfigured to control a display output device and a controllerconfigured to acquire data from an input device. Examples of the inputdevice include a keyboard, a mouse, and a touch panel. The input/outputunit 14 is configured to output display data to the display outputdevice under the control of the processor 11, and to acquire data inputby the user operating the input device. The display output device is,for example, a display device connected to the outside.

The image storage 19 is formed of, for example, an external storagedevice, such as a hard disk drive, or a flash memory. The image storage19 is configured to store an image registered by the user under controlof the information processing server 10. The image storage 19 followsinstructions of the information processing server 10 to receive an imagefrom the information processing server 10, store the image, and transmita read-out image to the information processing server 10. The imagestorage 19 is a device different from the information processing server10, but may be a part of the storage 12 of the information processingserver 10.

Next, functions provided by the information processing system 1 aredescribed. FIG. 2 is a block diagram for illustrating functionsimplemented by the information processing system 1. The informationprocessing system 1 includes an authentication module 50, an imageregistration module 51, a background identification module 53, and anidenticalness information output module 55. In addition, theidenticalness information output module 55 functionally includes afeature extraction module 56 and an identicalness information generationmodule 57. Those functions are implemented when the processor 11included in the information processing server 10 executes the programsstored in the storage 12 and controls the communication unit 13 andother components.

The authentication module 50 is configured to authenticate an account ofa user who accesses the information processing system 1. Morespecifically, the authentication module 50 acquires information requiredfor authentication including the account from the customer terminal 2operated by the user, and authenticates whether or not the account is aproper one. After the account has been authenticated, the subsequentcommunication between the customer terminal 2 and the informationprocessing server 10 is associated with the account. It is assumed thatthe user has created an account with respect to the informationprocessing system 1 in advance.

The image registration module 51 is configured to acquire an image froma user who accesses the information processing system 1 from a certainaccount, and store the acquired image in the image storage 19 inassociation with the account.

The background identification module 53 is configured to identify abackground area of the image registered from the account.

The identicalness information output module 55 is configured to outputidenticalness information, which indicates whether or not a user owninga first account serving as a query and a user owning a second accountbeing another account are identical, based on a background area of afirst image associated with the first account and a background area ofthe second image associated with the second account.

The feature extraction module 56 is configured to acquire, from each ofthe registered images, one global feature vector indicating a globalfeature of the background area of the image and a plurality of localfeature vectors indicating local features of the image.

The identicalness information generation module 57 is configured tooutput the identicalness information based on a first global featurevector acquired for the first image and a second global feature vectoracquired for the second image. The identicalness information generationmodule 57 is also configured to output the identicalness informationbased on a plurality of first local feature vectors acquired for thefirst image and a plurality of second local feature vectors acquired forthe second image. The identicalness information generation module 57 isalso configured to search for at least one of second imagescorresponding to the first image based on the background area of atleast one first image and the background areas of a plurality of secondimages, and to output the identicalness information based on the atleast one of second images corresponding to the at least one firstimage.

FIG. 3 is a flow chart for illustrating an example of processing of theimage registration module 51. First, the image registration module 51receives an image uploaded from the customer terminal 2 (Step S101). Theimage registration module identifies an account from which the image hasbeen transmitted (Step S102). In this case, the image registrationmodule 51 may identify the account from which the image has beentransmitted based on the account associated with the communication fromthe customer terminal 2, or may identify the account from which theimage has been transmitted based on information transmitted togetherwith the image. The image registration module 51 stores the receivedimage in the image storage 19 in association with the identified account(Step S103).

FIG. 4 is a view for illustrating an example of an image to beregistered. FIG. 4 is an example of an image to be registered in amarketplace service that allows customers to directly buy and sellproducts therebetween, and is an illustration of an image of a bagplaced in a room.

Next, processing for detecting a plurality of accounts owned by anidentical user is described. FIG. 5 is a flow chart for illustrating anexample of processing of the background identification module 53 and thefeature extraction module 56.

The processing illustrated in FIG. 5 is executed for each image. Inaddition, the processing illustrated in FIG. 5 may be performed eachtime the image registration module 51 receives an image to beregistered. In another case, images for which the processing illustratedin FIG. 5 has not been executed may be periodically detected, and theprocessing illustrated in FIG. 5 may be executed for each of thedetected images.

First, the background identification module 53 identifies the backgroundarea of the image to be processed (Step S201). The background area maybe identified by so-called semantic segmentation using a neural network,or may be identified by a so-called region proposal method using aneural network. Those methods are publicly known, and hence detaileddescriptions thereof are omitted.

When the background area is identified, the background identificationmodule 53 acquires an image obtained by filling an area (namely,foreground) other than the background area as an image (backgroundimage) of the background area of the image to be processed (Step S202).

FIG. 6 is a view for illustrating an example of the background image. Inthe background image, an area of a bag, which is the foreground, isfilled. In the following processing, the filled area is treated as anarea including no image, and is excluded from extraction targets of theglobal feature vector and the local feature vector.

When the background image is acquired, the feature extraction module 56calculates uniqueness of the background image (Step S203). Theuniqueness of the background image may be calculated by the featureextraction module 56 inputting the background image into a machinelearning model and acquiring output of the machine learning model as acalculation result. In this embodiment, the machine learning model is amachine learning model implemented with machine learning, for example,AdaBoost, a random forest, a neural network, a support vector machine(SVM), or a nearest neighbor discriminator.

The machine learning model is subjected to learning based on trainingdata including learning input images and label data in advance. Thetraining data includes: a learning input image obtained by enlarging orreducing the background image so that the background image has apredetermined number of pixels; and given label data indicating a levelof the uniqueness of the background image.

The uniqueness may be calculated without use of the machine learningmodel. For example, the level of the uniqueness may be calculated byobtaining a variance of a gradation value of the background image. Inthis case, as the background is closer to a single color, a variancevalue becomes smaller, and the uniqueness becomes lower. It is difficultto detect an ordinary pattern of, for example, a lattice, but it ispossible to calculate the uniqueness at high speed.

In another case, the uniqueness may be calculated based on backgroundimages similar to the background image for which the uniqueness is to becalculated. More specifically, an image search model including aplurality of background images that have already been acquired is builtin advance. Then, the feature extraction module 56 searches forbackground images similar to the background image for which theuniqueness is to be calculated through use of the image search model.The feature extraction module 56 calculates the uniqueness based on thenumber of similar background images found through the search or asimilarity between each of the similar background images and thebackground image for which the uniqueness is to be calculated. As thenumber of similar background images that have been found becomessmaller, or the similarity becomes smaller, the uniqueness becomeshigher.

When the background image has no uniqueness (the level of the uniquenessis lower than a determination threshold value) (N in Step S204), thefeature extraction module 56 excludes the image from which thisbackground image has been extracted from targets to be subjected todetermination of accounts owned by an identical user, which is describedbelow (Step S205), and the processing from Step S206 to Step S208 is notexecuted.

The processing from Step S203 to Step S205 is performed in order toexclude an ordinary (low in uniqueness) background image from processingtargets. The ordinary background image is highly likely to be includedin images of different users, and hence it is not appropriate to use theordinary background image to detect a plurality of accounts owned by anidentical user. Accordingly, those processing steps can improve accuracyin detection of a plurality of accounts owned by an identical user, andcan save calculation resources by skipping the processing relating tothe ordinary background image.

In this case, when the background image has uniqueness (the level of theuniqueness exceeds the determination threshold value) (Y in Step S204),the feature extraction module 56 extracts a plurality of local featurevectors from the background image, and stores the extracted localfeature vectors in association with the original image of the backgroundimage (Step S206). The local feature vectors may be stored in the imagestorage 19, or may be stored in the storage 12. Each of the plurality oflocal feature vectors indicates a local feature of the background image.The feature extraction module 56 may extract the local feature vectorsthrough use of a publicly known method, for example, SIFT, ORB, orBRISK.

The feature extraction module 56 also acquires a position of a point atwhich the local feature vector is extracted in the image together withthe local feature vector, and stores the position of the point as wellin association with the image. FIG. 7 is a view for schematicallyillustrating the extraction of the local feature vectors. In FIG. 7, theblack circles indicate the points at which the local feature vectors areextracted from the background image illustrated in FIG. 6. The localfeature vectors are extracted from the points exhibiting the localfeatures in the background image, and the number of local featurevectors varies depending on the background image. In the followingdescription, local feature vectors extracted from a background imagegenerated from a certain image are referred to as “local feature vectorsof the image.”

The feature extraction module 56 also extracts information other thanthe local feature vectors. More specifically, the feature extractionmodule 56 extracts a global feature vector from the background image,and stores the extracted global feature vector in association with theoriginal image of the background image (Step S207). In this case, thefeature extraction module 56 extracts one global feature vector from onebackground image. In the following description, a global feature vectorextracted from a background image generated from a certain image isreferred to as “global feature vector of the image.”

The feature extraction module 56 may extract the global feature vectorthrough use of the method of “Bag of Visual Words (BoVW).” In this case,the feature extraction module 56 may determine Visual Words based onbackground images having uniqueness among the background images relatingto all accounts and extract the global feature vector of each of thebackground images, or may determine Visual Words based on some of thebackground images. The processing method of BoVW is publicly known, andhence a detailed description of the processing is omitted. The featureextraction module 56 may extract the global feature vector based on thelocal feature vectors extracted in Step S206, or may extract the globalfeature vector based on local feature vectors extracted by a methoddifferent from that of Step S206. In another case, although the accuracyis lowered, the feature extraction module 56 may extract the globalfeature vector from an image in which the foreground is not filled.

In place of BoVW, the feature extraction module 56 may input abackground image to an encoder portion of an autoencoder and acquireoutput of the encoder portion as the global feature vector. In thiscase, it is assumed that a plurality of training images are input to theautoencoder in advance and a parameter of each node of the autoencoderis adjusted based on the output of the autoencoder and the trainingimages.

Now, the processing of the identicalness information generation module57 is described. The identicalness information generation module 57determines whether or not the first image and the second image have anidentical background in order to determine a certain account (firstaccount) and another account (second account) belong to an identicaluser. The first image is an image stored in association with the firstaccount by the image registration module 51, and the second image is animage stored in association with the second account by the imageregistration module 51. However, the first image and the second imagethat are to be subjected to the following processing are limited tothose determined to have uniqueness in the background image in StepS204.

FIG. 8 is a diagram for illustrating an outline of processing of theidenticalness information generation module 57. To facilitate thedescription, FIG. 8 is an illustration of an exemplary case in which onefirst image associated with the first account is used as a query imageto search a plurality of second images for a second image having abackground in common with the first image. The processing illustrated inFIG. 8 may be executed on each of the first images associated with thefirst account.

The identicalness information generation module 57 executes three-stageprocessing in order to reduce a processing load and improve accuracy atthe same time. In the first-stage processing, a group of second images(first candidate group) is generated by screening similar backgroundimages by a method having a low processing load. In the first-stageprocessing, a similar second image is detected based on the similaritybetween the global feature vector of the first image and the globalfeature vector of the second image. The detected second image is addedto the first candidate group.

The background image of the first image and the background image of thesecond image correspond to the first image and the second image,respectively, on a one-to-one basis, and hence in the first-stageprocessing, the background image of the first image and the backgroundimage of the second image may be detected in place of the first imageand the second image, respectively. The same applies to the followingprocessing.

In the second-stage processing, a group of second images (secondcandidate group) having a smaller number than the first candidate groupis generated by screening similar background images by a more accuratemethod. In the second-stage processing, a plurality of local featurevectors (first local feature vectors) of the first image and a pluralityof local feature vectors (second local feature vectors) of the secondimage are caused to match each other by a publicly known matchingmethod, and it may be determined whether they are similar to each otherbased on the number of sets of the first local feature vector and thesecond local feature vector that are considered to correspond to eachother.

In the third-stage processing, the second images are screened based onwhether or not a proper three-dimensional background can be obtainedfrom sets of the first local feature vector and the second local featurevector corresponding to each other. More specifically, in thethird-stage processing, from a plurality of sets, the three-dimensionalpositions of the points at which the first and second local featurevectors included in the sets are extracted are estimated, and it isdetermined whether a proper three-dimensional background has beenobtained based on whether or not the three-dimensional positions havebeen properly estimated. This determination is performed for each of thesecond images included in the second candidate group. The second imagedetermined to include an identical background is output as a finalsearch result.

FIG. 9 to FIG. 11 are flow charts for illustrating examples ofprocessing of the identicalness information generation module 57. FIG. 9to FIG. 11 indicate processing for identifying a set of a first imageand a second image that have an identical background image from aplurality of first images associated with the first account and thesecond image associated with the second account, and determining whetheror not the first account and the second account are owned by anidentical user based on the identified set. The first-stage processingis the processing of Step S305, the second-stage processing is theprocessing from

Step S311 to Step S317, and the third-stage processing is the processingfrom Step S321 to Step S327.

First, the identicalness information generation module 57 selects onefirst image from a plurality of images determined to have uniquenessamong a plurality of first images associated with the first account(Step S301). Subsequently, the identicalness information generationmodule 57 acquires, as the first global feature vector, a global featurevector stored in association with the selected first image (Step S302),and acquires, as the plurality of first local feature vectors, aplurality of local feature vectors stored in association with theselected first image (Step S303).

Then, the identicalness information generation module 57 calculates, foreach of the second images associated with the second account, thesimilarity between the first global feature vector and the second globalfeature vector associated with the second image. Of the plurality ofsecond images, a second image having a similarity higher than athreshold value is added to the first candidate group (Step S305). Thesimilarity is, for example, L2 norm, and a criterion of the similarityfor determining an image which is similar thereto is set to be looserthan that of the second-stage processing.

When the second image is added to the first candidate group, theidenticalness information generation module 57 selects one second imagebelonging to the first candidate group (Step S311). Then, theidenticalness information generation module 57 determinescorrespondences between the acquired plurality of first local featurevectors and the plurality of second local feature vectors associatedwith the selected second image (Step S312).

The publicly known matching method is used in determining thecorrespondences. For example, the identicalness information generationmodule 57 calculates a distance (corresponding to the similarity)between the first local feature vector and each of the plurality ofsecond local feature vectors by, for example, L2 norm. In addition, when“d1<d2×A” (where A is a constant equal to or larger than 0 and smallerthan 1) is satisfied between a second local feature vector having thesmallest distance (d1) and a second local feature vector having thesecond smallest distance (d2), the identicalness information generationmodule 57 determines the second local feature vector having the smallestdistance (d1) as the second local feature vector corresponding to thefirst local feature vector, and stores a set of the first local featurevector and the second local feature vector corresponding thereto in thestorage 12. In this case, the determined second local feature vector isnot to be determined to correspond to another first local featurevector.

As the matching method, the matching between the first local featurevector and the second local feature vector may be performed by, forexample, SuperGlue or another graph neural network.

FIG. 12 is a view for illustrating the correspondences between the firstand second local feature vectors. The upper image corresponds to onefirst image, and the lower image corresponds to one second image. Theblack circles of the upper image correspond to the first local featurevectors, and the black circles of the lower image correspond to thesecond local feature vectors. The black circles connected by each brokenline indicate the first and second local feature vectors correspondingto each other.

When the correspondences are determined, the identicalness informationgeneration module 57 determines whether or not the background image ofthe first image and the background image of the second image are similarto each other based on the correspondences (Step S313). Specifically,the identicalness information generation module 57 may determine thesimilitude based on whether or not the number of sets of the first localfeature vector and the second local feature vector that are consideredto correspond to each other exceeds a threshold value.

The identicalness information generation module 57 may also determinethe similitude based on whether or not a ratio of the number of sets tothe smaller number between the number of first local feature vectors andthe number of second local feature vectors exceeds a set thresholdvalue.

When it is determined that the background image of the first image andthe background image of the second image are not similar to each other(N in Step S313), the processing of Step S314 and Step S315 is skipped.Meanwhile, when it is determined that the background image of the firstimage and the background image of the second image are similar to eachother (Y in Step S313), the identicalness information generation module57 determines whether or not the background image of the first image andthe background image of the second image are extremely close to eachother (Step S314). More specifically, the identicalness informationgeneration module 57 determines that the background image of the firstimage and the background image of the second image are extremely closeto each other when the number of sets of the first and second localfeature vectors corresponding to each other is larger than a strictthreshold value and a sum or average of the distances between the firstlocal feature vectors and the second local feature vectors correspondingto each other is smaller than a strict distance threshold value. In thiscase, the strict threshold value is larger than the set threshold value.

When it is determined that the background image of the first image andthe background image of the second image are extremely close to eachother (Y in Step S314), the identicalness information generation module57 determines that the first image and the second image correspond toeach other, and stores the set of the first image and the second imagein the storage 12 (Step S319). Then, the identicalness informationgeneration module 57 advances to the processing of Step S326 by skippingthe third-stage processing.

When the backgrounds of the first image and the second image areextremely similar to each other, the identicalness informationgeneration module 57 determines that the first image and the secondimage have an identical background without performing the subsequentprocessing. Thus, the subsequent processing is not performed, and hencethe processing time is reduced. In addition, when the point of view of acamera is almost the same because of use of, for example, a tripod, itis possible to reduce such a fear that the relationship between thefirst account and the second account may be erroneously determined byerroneously determining that the first image and the second image do notcorrespond to each other in the third-stage processing.

Meanwhile, when it is not determined that the background image of thefirst image and the background image of the second image are extremelyclose to each other (N in Step S314), the identicalness informationgeneration module 57 adds the selected second image to the secondcandidate group, and stores the sets of the first local feature vectorand the second local feature vector corresponding to each other in thestorage 12 in association with the second image (Step S315). When thesecond images belonging to the first candidate group include a secondimage that has not been selected (N in Step S316), the identicalnessinformation generation module 57 selects the next second image from thefirst candidate group (Step S317), and repeatedly performs theprocessing of Step S312 and the subsequent steps.

When all of the second images belonging to the first candidate grouphave been selected (Y in Step S316), the second candidate group isdetermined, and the procedure advances to the third-stage processing ofStep S321 and the subsequent steps.

When the second image is added to the second candidate group, theidenticalness information generation module 57 selects one second imagebelonging to the second candidate group (Step S321). Then, theidenticalness information generation module 57 calculates, based on theplurality of sets stored in association with the selected second image,a three-dimensional position of a point corresponding to each of thesets (Step S322). In other words, the identicalness informationgeneration module 57 estimates the three-dimensional position of a pointat which the first and second local feature vectors are extracted foreach of the plurality of sets based on a position at which the firstlocal feature vector has been extracted in the first image and aposition at which the second local feature vector has been extracted inthe second image.

The three-dimensional position may be estimated through use of a conceptof so-called triangulation. FIG. 13 is a view for illustratingcalculation of the three-dimensional position.

More specifically, first, the identicalness information generationmodule 57 estimates points e1 and e2 of view and photographingdirections (see the arrows extending from the points e1 and e2 of view)with which the images have been acquired, based on positions (see pointsPi1 and Pi2 of FIG. 13) in the first and second images (see images m1and m2 of FIG. 13) from which the first and second local feature vectorsincluded in each of the plurality of sets have been extracted. Then, theidenticalness information generation module 57 uses a direct lineartransform (DLT) method based on the points of view, the photographingdirections, and the positions (points) at which the first and secondlocal feature vectors have been extracted, to thereby obtain thethree-dimensional position of a point (see point Pr of FIG. 13)corresponding to those points. A method of obtaining thethree-dimensional position of a point at which local feature vectorscorresponding to each other are extracted in a plurality of images ispublicly known, and hence a more detailed description thereof isomitted. This method is also used in, for example, software forimplementing an SfM, and the identicalness information generation module57 may calculate the three-dimensional position of a point for each ofthe plurality of sets by executing this software.

When the three-dimensional position of the point is calculated, theidenticalness information generation module 57 determines whether or notthe three-dimensional position has been properly estimated. Morespecifically, first, the identicalness information generation module 57reprojects the point onto the first image and the second image based onthe calculated three-dimensional position of the point, and calculatesreprojection errors between positions of the reprojected point andpositions of original points in the first image and the second image(Step S323). In this case, the positions of the original points in thefirst and second images are the positions at which the first and secondlocal feature vectors have been extracted in the first and secondimages, respectively. In other words, the reprojection errors are: adistance between a projected point at which the three-dimensional pointhas been projected onto the first image and the point at which the firstlocal feature vector corresponding to the projected point has beenextracted; and a distance between a projected point at which thethree-dimensional point has been projected onto the second image and thepoint at which the second local feature vector corresponding to theprojected point has been extracted.

The identicalness information generation module 57 calculates a sum ofthe reprojection errors calculated for each of the plurality of sets,and determines whether or not the sum of the reprojection errors fallswithin a predetermined range (is smaller than a determination thresholdvalue) (Step S324). When the sum of the reprojection errors falls withinthe predetermined range (Y in Step S324), the identicalness informationgeneration module 57 determines that the first image and the secondimage correspond to each other, and stores the set of the first imageand the second image in the storage 12 (Step S325). When the sum of thereprojection errors does not fall within the predetermined range (islarger than the determination threshold value), Step S325 is skipped. Inplace of the determination based on whether or not the sum exceeds thethreshold value, the determination may be performed based on the averageor a variance of the reprojection errors.

When the second images belonging to the second candidate group include asecond image that has not been selected (N in Step S326), theidenticalness information generation module 57 selects the next secondimage from the second candidate group (Step S327), and repeatedlyperforms the processing of Step S322 and the subsequent steps.Meanwhile, when all of the second images belonging to the secondcandidate group have been selected (Y in Step S326), the third-stageprocessing is brought to an end, and the procedure advances to theprocessing of Step S330 and the subsequent steps.

In Step S330, the identicalness information generation module 57determines whether all the images of at least one of first images thatare associated with the first account and have uniqueness have beenselected. When there is an image that has not yet been selected (N inStep S330), the identicalness information generation module 57 selectsthe next first image among the plurality of first images that areassociated with the first account and have uniqueness (Step S331), andrepeatedly performs the processing of Step 5302 and the subsequentsteps.

Meanwhile, when all the first images have been selected (Y in StepS330), the identicalness information generation module 57 generatesidenticalness information indicating whether or not the user owning thefirst account and the user owning the second account are identical toeach other based on the sets of the first image and the second imagethat are stored in the storage 12 (Step S332). The plurality of setseach including the first image and the second image are informationequivalent to at least one first image and at least one of second imagescorresponding to the at least one first image.

FIG. 14 is a diagram for illustrating an example of correspondencesbetween the first images and the second images. FIG. 14 indicatescombinations of images that have been considered to have the samebackground and determined to correspond to each other in the firstaccount and the second account. The lines connecting the images indicatecorrespondences between the images. In Step S332, for example, when thenumber of sets or a value obtained by dividing the number of sets by thesum of the number of first images and second images exceeds apredetermined threshold value, the identicalness information generationmodule 57 determines that the first account and the second account areowned by an identical user, and may create identicalness informationindicating the determination result. Through the determination using thecorrespondences of a plurality of images in such a manner, it ispossible to prevent erroneous determination ascribable to, for example,an accidental match.

The processing illustrated in FIG. 9 to FIG. 11 is executed for aplurality of second accounts that are different from one another. Inview of this, the identicalness information generation module 57 maygenerate identicalness information based on the number of secondaccounts determined to match the first account. More specifically, theidenticalness information generation module 57 determines whether or notthe first account and the second account match each other for each ofthe plurality of second accounts through use of the same method as themethod of generating identicalness information indicating whether or notthe two accounts are identical to each other in Step S332. Then, afterthe matching determination is performed for the plurality of secondaccounts in Step S332, the identicalness information generation module57 generates identicalness information indicating whether or not theuser owning the first account and users owning the plurality of secondaccounts are identical to each other based on the number of secondaccounts determined to match the first account.

For example, the identicalness information generation module 57 maygenerate identicalness information indicating that the user owning thefirst account and the users owning the plurality of second accounts areidentical to each other when the number of second accounts matching thefirst account is smaller than an account threshold value (for example,an integer of 3 or more), and is not required to generate identicalnessinformation indicating identicalness when the number of second accountsthat match the first account is equal to or larger than the accountthreshold value. Thus, for example, when a background image actuallyhaving low uniqueness is targeted for the processing illustrated in FIG.9 to FIG. 11, it is possible to prevent the first and second accountsactually owned by different users from being erroneously determined tobe identical to each other.

When it is determined that the first image and the second image have thesame background and correspond to each other, the identicalnessinformation generation module 57 may determine , in place of Step S325and Step S319, that an identical user owns the first account associatedwith the first image and the second account associated with the secondimage to generate identicalness information. In this case, theprocessing illustrated in FIG. 9 to FIG. 11 is not executed thereafter.With this processing, it is possible to reduce the processing loadirrespective of some decrease in accuracy.

While there have been described what are at present considered to becertain embodiments of the invention, it will be understood that variousmodifications may be made thereto, and it is intended that the appendedclaims cover all such modifications as fall within the true spirit andscope of the invention.

What is claimed is:
 1. An information processing device, comprising: atleast one processor; and at least one memory device that stores aplurality of instructions which, when executed by the at least oneprocessor, causes the at least one processor to: identify a backgroundarea of a first image registered from a first account and a backgroundarea of a second image registered from a second account; and outputidenticalness information indicating whether a user owning the firstaccount and a user owning the second account are identical to each otherbased on the background area of the first image and the background areaof the second image.
 2. The information processing device according toclaim 1, wherein the plurality of instructions cause the at least oneprocessor to: acquire a plurality of first local feature vectors eachindicating a local feature of the first image; acquire a plurality ofsecond local feature vectors each indicating a local feature of thesecond image; and output the identicalness information based on resultsof searching for the second local feature vectors that correspond to theplurality of first local feature vectors, respectively.
 3. Theinformation processing device according to claim 2, wherein theplurality of instructions cause the at least one processor to: identifythe background area of the first image and the background area of eachof a plurality of second images; select a plurality of candidate imageseach having the background area similar to the background area of thefirst image from among the plurality of second images based on a firstglobal feature vector extracted from the first image and a plurality ofsecond global feature vectors extracted from the plurality of secondimages, respectively; acquire the plurality of first local featurevectors, each indicating the local feature of the first image and theplurality of second local feature vectors, each indicating the localfeature of any one of the plurality of candidate images; and output theidenticalness information indicating whether the user owning the firstaccount and the user owning the second account are identical to eachother.
 4. The information processing device according to claim 2,wherein the plurality of instructions cause the at least one processorto: estimate a three-dimensional positions for each of a plurality ofpoints, at which at least a part of the plurality of first local featurevectors are extracted, based on positions at which at least a part ofthe plurality of first local feature vectors have been extracted in thefirst image and positions at which the second local feature vectorscorresponding to the plurality of first local feature vectors,respectively, have been extracted in the second image; and output theidenticalness information based on the estimated three-dimensionalpositions of the plurality of points.
 5. The information processingdevice according to claim 1, wherein the plurality of instructions causethe at least one processor to: identify a background area of at leastone first image and a background area of each of a plurality of secondimages; search for at least one of second images corresponding to the atleast one first image based on the background area of the at least onefirst image and the background areas of the plurality of second images;and output the identicalness information based on the at least one ofsecond images corresponding to the at least one first image.
 6. Theinformation processing device according to claim 1, wherein theidenticalness information comprises a result of determination of whetherthe user owning the first account and the user owning the second accountare identical to each other.
 7. The information processing deviceaccording to claim 1, wherein the identicalness information indicates aprobability that the user owning the first account and the user owningthe second account are identical to each other.
 8. An informationprocessing method, comprising: identifying, with at least one processoroperating with a memory device in a system, a background area of a firstimage registered from a first account and a background area of a secondimage registered from a second account; and outputting, with the atleast one processor operating with the memory device in the system,identicalness information indicating whether a user owning the firstaccount and a user owning the second account are identical to each otherbased on the background area of the first image and the background areaof the second image.
 9. A non-transitory computer readable storagemedium storing a plurality of instructions, wherein when executed by atleast one processor, the plurality of instructions cause the at leastone processor to: identify a background area of a first image registeredfrom a first account and a background area of a second image registeredfrom a second account; and output identicalness information indicatingwhether a user owning the first account and a user owning the secondaccount are identical to each other based on the background area of thefirst image and the background area of the second image.